My Genes Made Me Do It - Heritability in Addictions

Written by Stanton Peele

Such heritability figures may seem quite remarkable, even incredible. Behavior geneticists report that half of the basis of divorce, bulimia and attitudes about punishing criminals is biologically inherited, comparable to or higher than the figures calculated for depression, obesity, and anxiety. Almost any trait seemingly yields a minimum heritability figure around 30 percent. The heritability index acts like a scale that reads 30 pounds when empty and adds 30 pounds to everything placed on it!

Believing that basic traits are largely predetermined at birth could have tremendous implications for our self-conceptions and public policies. Not long ago, an announcement for a government conference, for example, suggested that violence could be prevented by treating with drugs children with certain genetic profiles. Or, parents of children with an alcoholic heritage may tell the children never to drink because they're destined to be alcoholics. But such children, in expecting to become violent or drink excessively, may enact a self-fulfilling prophecy. Indeed, this is known to be the case. People who believe they are alcoholic drink more when told a beverage contains alcohol - even if it doesn't.

Believing the heritability figures developed by behavioral geneticists leads to an important conclusion: Most people must then be overestimating how much daily impact they have on important areas of children's development. Why ask Junior to turn off the TV set if television viewing is inherited, as some claim? What, exactly, can parents accomplish if traits such as prejudice are largely inherited? It would not seem to matter what values we attempt to convey to our children. Likewise, if violence is mostly inbred, then it doesn't make much sense to try to teach our kids to behave properly.

View from the Genome

The vision of humanity generated by statistical research on behavior genetics seems to enhance the passivity and fatalism many people are already saddled with. Yet evidence gathered by psychologist Martin Seligman and others indicates that "learned helplessness" - or believing one cannot influence one's destiny - is a major factor in depression. The opposite state of mind occurs when people believe they control what happens to them. Called self-efficacy, it is a major contributor to psychological well-being and successful functioning.

Is there a connection between the increase in depression and other emotional disorders in 20th-century America and our outlook as a society? If so, then the growing belief that our behavior is not ours to determine could have extremely negative consequences. As well as attacking our own sense of personal self-determination, it may make us less able to disapprove of the misbehavior of others. After all, if people are born to be alcoholic or violent, how can they be punished when they translate these dispositions into action?

Jerome Kagan, whose studies provide a close-up of the interaction of nature and nurture and how it plays out in real life, worries that Americans are too quick to accept that behavior is predetermined. He has studied the temperaments of infants and children and found distinctive differences at birth - and even before. Some babies are outgoing, seemingly at home in the world. And some recoil from the environment; their nervous systems are overly excitable in response to stimulation. Do such findings mean children born with a highly reactive nervous system will grow into withdrawn adults? Will extremely fearless children grow into violent criminals?

In fact, less than half of reactive infants (those who more frequently fret and cry) are fearful children at the age of two. It all depends on the actions parents take in response to their infant.

Kagan fears people will read too much into children's supposedly biological dispositions, and make unwarranted predictions about how they will develop: "It would be unethical to tell parents that their 3-year-old son is at serious risk for delinquent behavior." People who are more fearful or fearless than average have choices about the paths their lives will take like everyone else.

Nature, Nurture: Let's Call the Whole Thing Off

How much freedom each person has to develop returns us to the issue of whether nature and nurture can be separated. Thinking of traits as being either genetically or environmentally caused cripples our understanding of human development. As Kagan's puts it, "To ask what proportion of personality is genetic rather than environmental is like asking what proportion of a blizzard is due to cold temperature rather than humidity."

A more accurate model is one in which chains of events split into further layers of possible paths. Let's return to alcoholism. Drinking produces greater mood change for some people. Those who find alcohol to serve a strong palliative function will be more likely to use it to calm themselves. For example, if they are highly anxious, alcohol may tranquilize them. But even this tranquilizing effect, we should recognize, is strongly influenced by social learning.